1. Field of Invention
This invention relates to a new and improved signal amplifier system for use with controlled carrier signal measuring sensor/transducers of the variable impedance type.
More specifically, the invention relates to a signal amplifier system for improved processing of the electric signal developed across a sensor/transducer of the variable impedance type used in the measurement of certain physical parameters such as displacement, force, torsion, temperature, weight, size, pressure, vibration and the like. The physical parameter to be measured causes a variation in the electrical impedance of the variable impedance sensor/transducer which variation in turn produces a change in the nature of an oscillatory carrier voltage signal appearing across the sensor/transducer during the measurement. Upon being sensed, the change in the carrier voltage oscillatory signal provides a measure of the displacement, size, spacing, or other physical characteristic such as frequency, flow, etc. of the physical parameter being measured. Thus, it will be appreciated that the signal amplifier system serves to sense the variation in impedance caused by the physical parameter being measured by converting the variation into a change in the nature of the oscillatory carrier voltage signal whose value then is detected and displayed and is representive of the physical parameter being measured.
2. Background Problem
One of the more difficult problems to overcome in a variable impedance type measuring system is to obtain a linear output which is isolated from and independent of any stray capacitance coupling effects. While there are a number of known, prior art amplifier systems for processing signals derived from variable impedance type sensor/transducers, most of these known systems require the use of an elaborate array of driven guard shields, isolation transformers, and/or additional floating power supplies all of which complicate construction, maintenance and operation of the equipment as well as add to its expense, size and weight. One such known prior art system, for example, is described in U.S. Pat. No. 3,626,287 issued Dec. 7, 1971 for a "System for Responding to Changes in Capacitance of a Sensing Capacitor". In order to provide an improved signal amplifier system for controlled carrier signal measuring sensor/transducers of the variable impedance type having comparable performance and reliability but without requiring their undue circuit complexity, the present invention was devised.